Using a mobile phone before going to bed can damage your health, according to a major study.
It claims that radiation from the handset can cause insomnia and headaches as well as cutting the time spent in deep sleep.
Failing to get enough sleep can lead to depression, lack of concentration and personality changes.
In teenagers and young children, lack of sleep can result in attention disorders and poor academic performance.
The research, carried out by scientists funded by handset manufacturers, showed that using the handsets before bed causes people to take longer to reach the deeper stages of sleep and to spend less time in them.
Deep sleep is essential as it is the time when the body rejuvenates cells and repairs damage suffered during the day.
Dr Chris Idzikowski, director of the Edinburgh Sleep Centre, said: "There is now more than sufficient evidence from a large number of reputable investigators who are finding that mobile phone exposure an hour before sleep adversely affects deep sleep."
In the study scientists examined the sleep patterns of 36 women and 35 men aged 18 to 45.
Some were exposed to radiation that mimicked what a person receives when using a mobile phone. The others received none.
The first group took longer to enter the first of the deeper stages of sleep and spent less time in the deepest one.
The scientists concluded: "The study indicates that during laboratory exposure to 884 MHz wireless signals components of sleep believed to be important for recovery from daily wear and tear are adversely affected."
The findings will shock many parents whose children routinely chat to friends on their mobiles before sleep.
The study, by scientists from the Karolinska Institute and Uppsala University in Sweden and from Wayne State University in Michigan, is thought to be the most comprehensive of its kind.
The research was published by the Massachusetts Institute of Technology and funded by the Mobile Manufacturers Forum.
